Device and Method for Measuring a Shot Force Exerted on a Movable Game Device

ABSTRACT

For measuring a shot force exerted on a movable game device, a time curve of the acceleration during the shot or of the pressure within the game device during the shot is recorded and processed to obtain an energy measure, said energy measure then serving to provide information about the shot force.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.11/460,565, filed Jul. 27, 2006, which is incorporated herein in itsentirety by reference, which claims priority from German PatentApplication No. 102005036355.5, which was filed on Jul. 29, 2005, theentirety of which is herein incorporated by this reference thereto.

TECHNICAL FIELD

The present invention relates to movable devices and in particular togame devices such as balls, and to concepts for detecting any contact ofan object with the movable device.

BACKGROUND

For quite some time, various interest groups have wished to study andunderstand the sequence of movements of moving objects and/or persons,which requires an exact indication of the object's position in space andtime. What is of particular interest here are, among other things, gameballs, in particular in commercialized types of sport, such asfootballs, or soccer balls, which are highly accelerated inthree-dimensional space, as well as tennis or golf balls. The questionof who was the last to touch the object of the game, how it was hit andin which direction it was accelerated further may be decisive for theoutcome of the game, depending on the type of game.

Game devices that are used in high-performance sports, such as tennisballs, golf balls, footballs and the like, nowadays can be acceleratedto extremely high speeds, so that the detection of the object during themovement requires highly sophisticated technology. The technical meansemployed so far—mainly cameras—either completely fail to meet therequirements set forth above, or meet them only to an insufficientdegree; also the methods, hitherto known, for position finding by meansof various transmitter and receiver combinations still leave a largeerror margin with regard to the spatial resolution of the positionindication, with regard to the ease of use of the transmitter/receivercomponents required, and above all with regard to evaluating the dataobtained by means of the transmitter/receiver system, so that it is notyet possible, or at least requires a large amount of effort, to evaluatethe results obtained from this data as fast as possible.

It is not only in the field of commercial sports, where movable gamedevices maybe employed, but it is also in the personal field that usershave become more and more used to electronic devices indicating variousof information to give a user feedback as to how he/she has affected anobject, or to provide him/her with information about how a player hasaffected a gaming device.

Current statistics methods in commercial applications, such as of theGerman first football division (Bundesliga), work with recordingrelatively simple statistics, such as the percentage of ball contacts ofa team or the number of corners, free kicks or fouls.

On the other hand, there have been means, for example in tennis, wherethere is a very plannable, clearly arranged environment with only twoplayers, which measure, for example, the speed of the tennis ball at theserve, such that a viewer is in a position to assess whether a serve was“hard” or “soft”.

What is problematic about such speed measurements which may occur byoptical methods is the fact that they do not function within anenvironment where there is a muddle of players, such as on a footballpitch where there are not only two persons being active, but 22 persons,who, in addition unlike in tennis for a serve are not positioned in moreor less the same place but may form any constellation on the pitch. Onthe other hand, particularly in football, it is interesting, both forthe feedback of the players in training and for the viewers to know, forexample, how a shot actually came about and/or how large the force ofthe shot was.

Thus, kicking a ball in football or soccer or hitting a ball in tennisrepresents the actual “base” impact, as it were, on the game devicewhich is always decisive of how the game continues, since ultimatelyeverything is about doing something with the movable game device, suchas playing it into an opponent's field (as in tennis) or moving it intoa goal (as in football, or soccer) or into a basket (as in basketball)or to cause it to contact the floor of the opponent's pitch (as involleyball). Due to the difficulty of the continuously changingconstellations in dynamic games, in particular team games, however alsoin tennis when no serve is currently played, but the ball is played inone move, external speed measurements will fail, which has lead to thefact that there are currently no shot force detection systems that couldbe employed in a flexible manner.

On the other hand, for the field of sports, but also for the field ofleisure, there is a further limitation resulting from the fact thatthese fields are highly commercialized. All systems providing additionalinformation, in particular when they are intended for leisure of forleisure sports, must enable to be offered at a low price since they areobjects which a user never “absolutely needs” but might like to haveanyway. Particularly in such a market, it is decisive to be able tooffer a robust system at low price. For example, a system must notrequire a high level of maintenance or of equipment such as, forexample, a speed measurement system for measuring the serve of a tennisplayer. Due to the relatively high cost associated, a small tennis clubwould never acquire such a system for training purposes, which applieseven more to a private person who wishes to play tennis in a slightlymore ambitioned manner in his/her leisure time.

It is the object of the present invention to provide a concept formeasuring a shot force exerted on a movable game device, the conceptbeing applicable in a flexible manner while being low in expense.

In accordance with a first aspect, the invention provides a device formeasuring a shot force exerted on a movable game device, including:

a provider for providing a time curve, which occurs when the game deviceis impacted by an object, of an acceleration acting upon the object, ora time curve of a pressure of the game device;

a processor for processing the time curve of the acceleration or thetime curve of the pressure to obtain an energy measure which depends onan energy transferred onto the object by the shot;

a provider for providing information about the shot force on the basisof the energy measure.

In accordance with a second aspect, the invention provides a movablegame device including:

an acceleration sensor for providing a time curve of an acceleration, ora pressure sensor for providing a time curve of a pressure of the gamedevice which occurs while an object impacts the game device; and

an outputter for outputting the time curve of the acceleration orpressure.

In accordance with a third aspect, the invention provides a method formeasuring a shot force exerted on a movable game device, the methodincluding the steps of:

providing a time curve, which occurs when the game device is impacted byan object, of an acceleration acting upon the object, or a time curve ofa pressure of the game device;

processing the time curve of the acceleration or the time curve of thepressure to obtain an energy measure which depends on an energytransferred onto the object by the shot;

providing information about the shot force on the basis of the energymeasure.

In accordance with a fourth aspect, the invention provides a computerprogram having a program code for performing the method for measuring ashot force exerted on a movable game device, the method including thesteps of:

-   -   providing a time curve, which occurs when the game device is        impacted by an object, of an acceleration acting upon the        object, or a time curve of a pressure of the game device;    -   processing the time curve of the acceleration or the time curve        of the pressure to obtain an energy measure which depends on an        energy transferred onto the object by the shot;    -   providing information about the shot force on the basis of the        energy measure,

when the program runs on a computer.

The present invention is based on the findings that a shot-forcemeasurement which is accurate, low in maintenance and, at the same time,may be used in a flexible manner may be achieved in that a time curve ofan acceleration or a time curve of an internal pressure of a movablegame device is provided so as then to process this time curve,specifically with the aim of obtaining a measure of energy which dependson the energy transmitted to the object by the shot. In addition, ameans for providing information about the force of the shot is providedwhich uses the synergy measure for determining the force of the shot.Thus, in accordance with the invention, what is performed is not directspeed measurement but, in preferred embodiments, at the most an indirectspeed measurement, to the effect that a temporal acceleration curve anda temporal pressure curve are detected, and that is these time curves,or temporal curves, are processed to obtain a measure of energy, that issome quantity which is somehow connected to the energy in a linear ornon-linear or in some other manner. This measure is then used inaccordance with the invention to provide force-of-shot information. Thisforce-of-shot information may be a quantitative value which is, however,free from units, e.g. on a scale between 1 and 10, or it may be a valueon an open-ended scale, or it may be a value representing a forceexerted on the movable game device at the time of the shot, or it may bean energy value, i.e. a value of the energy imparted on the movable gamedevice at the shot.

Alternatively, the shot force may also be an indication of lengthproviding a measure of how far the ball would have flown, for example,if the ball had been shot at an optimum angle and without any rotation.Such a shot-force result is interesting, in particular, for ball sportssuch as soccer or American football, since to the players there, ameasure of length, for example how far a pass or kickout will have gone,means more than quantitative values or physical force or energy units.However, for a comparison with other players, the non-unit quantitativescale is highly interesting, whether it is finite or open-ended.

In preferred embodiments, ball contacts are also detected. Here, variouscomponents may be employed for both tasks. To this end, the use of twosignals having different signal speeds is ideal to achieve a robust butnevertheless efficient and accurate detection of a contact with amovable device. Thus, in accordance with the invention, a detectorwithin the movable device, e.g. in a football, detects whether anobject, such as a player's leg, is located in the vicinity of thefootball. This is effected, for example, by pressure, acceleration orvibration measurement or by non-contact measurement.

Once a detection has been made to the effect that the object is locatedin the vicinity of the movable device, the transmitter module iscontrolled to transmit two signals having different signal speeds. Areceiver device connected to the object will detect the first signal andthen wait for a certain time period for reception of the second signalhaving a lower signal speed. If the signal having the lower signal speedis detected within the predetermined time period which starts uponreception of the first, fast signal, it shall be assumed that the objectwhich has received both the first and, within the predetermined timeperiod, also the second signal, was in contact with the movable device.This is reflected in that a detector which has detected reception of thesecond signal within the predetermined time period provides a detectoroutput signal, a memory subsequently storing the fact that there hasbeen a detector output signal, i.e. that it is very likely for a ballcontact to have occurred. Alternatively or in addition, an absolutemoment in time at which the detector signal has occurred may be storedin the memory, so that when one thinks of a football match, a sequenceof moments result which may then, e.g. after a match or during a match,be read out to ascertain, as a function thereof, how many ball contactsa player had, or generally speaking, how many contacts an object hadwith the movable device.

If one assumes that, e.g., several football players are near a ball, thefast signal will be detected by several receiver devices. However, ifthe predetermined time duration is selected such that it is very likelythat really only that receiver device which is located closest to themovable device can receive the second signal within the predeterminedtime period, while receiver devices which are more remote will alsoreceive the second signal, but only after the predetermined timeduration has expired, no ball contact will be registered for thoseplayers.

By setting the predetermined time duration in the receiver devices worn,or carried, by the player, it is thus possible to set the accuracyand/or the range to be detected. For this purpose, no access to the ballitself is required.

In addition, the use of two signals of different speeds allows todispense with any complicated and, thus, failure-prone electronics inthe ball itself. One only needs to make sure that the ball has aproximity detector which operates in a contact-controlled or non-contactmanner and which will then control the transmission of the two signalsof different delay times. Thus, no complicated electronics are requiredwithin the ball itself, which is a considerable advantage in particularsince the forces and accelerations acting on the ball may be huge, sothat there is a very rough environment for there to be an electronicsystem within the ball.

On the receiver side, no personal identification or the like isrequired, which is of considerable advantage—particularly if oneconsiders that what is dealt with here is a mass product, i.e. that mayplayers are to be provided with receiver devices—since thus, allreceiver devices may operate in an identical manner and do not requireany specific identification, which also renders the receiver devicessimple and low in or even completely free from maintenance. In addition,a simple and robust structure also ensures safety from tampering.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe accompanying drawing, in which:

FIG. 1 is a schematic sketch of a pitch including a movable device andseveral objects provided with receivers;

FIG. 2 depicts a player with a football as an example of a movabledevice;

FIG. 3 is a schematic system sketch;

FIG. 4 a is a more detailed view of the functional groups within themovable device;

FIG. 4 b is a more detailed representation of the transmitter module ofFIG. 4 a;

FIG. 5 a is a block diagram representation of the receiver device; and

FIG. 5 b is a more detailed representation of the receiver device ofFIG. 5 a;

FIG. 6 a depicts a qualitative schematic curve of the acceleration overtime during a shot;

FIG. 6 b depicts a qualitative curve of the speed over time during ashot;

FIG. 6 c shows a qualitative curve of the force exerted on the movablegame device during a shot,

FIG. 6 d shows a qualitative curve of the force as a function of thedistance covered, the force being exerted on a movable game deviceduring a shot;

FIG. 6 e shows a preferred allocation table between the energy measureand the force of the shot;

FIG. 7 shows a qualitative curve of the internal pressure of a movablegame device;

FIG. 8 shows a group of straight lines for determining the shot forceusing the idle-state internal pressure as the parameter;

FIG. 9 shows a schematic block diagram of the inventive device formeasuring a force of shot exerted on a movable game device; and

FIG. 10 shows a flow diagram for a preferred force-of-shot measurementby means of a temporal pressure curve.

DETAILED DESCRIPTION

To improve one's skills in a ball game or to be able to compare oneselfto other players, objective data must be obtained in a simple manner.This data must be visualized such that a training feedback or acomparison to other players is possible. To this end, respectivecomponents are provided within the game device, and, if need be, a datadetection device including a display unit is provided.

In a low-cost system, recognition of a person cannot be effected viadelay times of the radio signals. To this end, the incoming radiosignals would have to be compared to a highly accurate time reference.Also, a network would have to be built within which all times measuredare compared to determine that player who is closest to the ball.Therefore, one concludes, from the transmission of a radio signal and anacoustic signal, as to who had the last ball contact.

By measuring the forces acting on the game device, one may also inferthe shot force or the rotational speed of the game device. If thisentails an energy observation, the individual player can learn tocontrol his/her influence on the game device.

Further advantages result from the further claims and subclaims and fromthe following description.

Before the invention will be described in detail, it shall be pointedout that it is not limited to the particular components of the device orto the procedure discussed, since these components and methods may vary.The expressions used here are merely intended to describe particularembodiments, and are not used by way of limitation. If the singular formor indefinite articles are used in the description and in the claims,they also relate to the plural form of these elements, unless theoverall context clearly indicates otherwise. The same applies in theopposite direction.

FIG. 3 shows a schematic system sketch. In particular, it shows a devicefor detecting the force and/or motion ratios on a game device 7, such asa ball, an assembly 15 being provided in the ball which is populatedwith several electronic components. Instead of the assembly, theelectronic components may also be disposed on the ball's jacket, forexample on the inside, or be suspended within the center of the ball.

At least one of the following electronic components is provided withinthe game device:

-   -   a transmitter 4 for acoustic or ultrasonic waves for        transmitting an acoustic signal,    -   a pressure sensor 10,    -   an acceleration sensor,    -   at least one Hall sensor 16,    -   at least two magnetoresistive sensors,    -   at least two coils.

The electronic components are in connection with a receiver 2 viatransmitter 4 for the acoustic or ultrasonic waves, or at least via aradio transmitter 3, for example via radio 1, for example to transferthe data detected by the electronic components. In addition, amicrocontroller 11 is provided for processing the data. This data canthen be transferred to a data detection device 12. An evaluation unit 13is provided for evaluating the data detected which is presented, if needbe, on a display unit 14. Data detection device 12 preferably isassociated with at least one player 6, preferably however with allplayers of a game to thereby perform a localization, for example, of thenearest player, as will be explained later on.

For some games, such as in a football match, it is often interesting toknow who had the most ball contacts. To determine this, one mustascertain, during the ball contact, who has touched the ball.

In a low-cost system, recognition of the person cannot be performed viadelay times of the radio signals. To this end, the arriving radiosignals would have to be compared with a highly accurate time reference,and a network would have to be built wherein all measured times arecompared in order to determine that player who is located closest to theball. Alternatively, the field strength of the transmitter at the ballcould be used to estimate a distance. However, this is imprecise.

To keep cost low, the delay time of sound is measured within the device.To this end, game device 7 emits, when recognizing a force being exertedupon it, an acoustic signal as a sound or ultrasound by a transmitter 4.At the same time, a radio transmitter 3 transmits a radio signal. Thereceiver 2 of a data detection device associated with player 6 registersthe acoustic signal and also the radio signal. The time differenceyields the distance from the ball. As soon as the radio signal isrecognized, the acoustic signal is awaited to arrive for 5 ms. If anacoustic impulse is recognized within this time period, one may assumethat receiver 2 of the data detection device 12 associated with player 6is spaced away from the ball by 1.5 meters at a maximum. It is then verylikely that this player has touched the ball. Preferably, each player 6carries, or wears, such a receiver. The number of acoustic impulsesrecognized is counted and displayed. Using this information and the hourof the event, one may then determine, in a subsequent interplay of alldata of all data detection units 12, how many ball contacts a player 6had. It is even possible to make statistic statements about howsuccessful passes were, since the target of a pass may be determined bya time comparison. This may be used to detect the following, forexample:

-   -   Who lost the ball how many times to the opponent?    -   Were the ball contacts constant over the playing time and was        there a drop in performance?    -   Who played how many passes to whom?    -   How often did a move pass several players of the same team?

The evaluation unit 13 thus has a means for evaluating whether anacoustic signal of transmitter 4 for the ball or ultrasonic wavesarrives within a predetermined time period after the arrival of theradio signal.

An inventive device for measuring a shot force exerted on a movable gamedevice is depicted in FIG. 9. The device includes a means 90 forproviding a time curve of an acceleration or an (internal) pressure of amovable game device, the time curve occurring when there is an impact onthe game device caused by a shot.

Depending on the type of sport, the object acting upon the movable gamedevice is a tennis racket, a leg of a football player, a hand of ahandball player, a table tennis paddle, etc., if the movable game deviceis a ball. Because of the fact that an object acts upon the movable gamedevice within the framework of a shot, an acceleration is exerted uponthe movable game device which—it being assumed that the movable objectwas at rest before—was zero, and which, at a time t₀ at which the objecthits the game device, will suddenly increase and will decrease, as isshown in FIG. 6 a, until a time t₁ at which the movable game deviceleaves the object that has impacted the movable game device.

This drop at time t₁ may be more or less abrupt, or the case may occurwhere the acceleration curve a(t) relatively “softly” approximates thevalue of zero, at which a constant speed is achieved which will becomenegative at some point in time due to the deceleration caused by airfriction. The deceleration of the movable game device due to friction orcatching objects is initially irrelevant to the force-of-shotmeasurement, or is to be taken into account in dependence on thedefinition of the force of the shot. The latter case will occur when,for example, a distance over which a football would fly is indicated inmeters as the force of the shot. Then, the deceleration of the gamedevice by air friction would have to be taken into account, specificallyit would have to be taken into account on the basis of the energymeasure when calculating the information about the force of the shot.

Specifically, the device depicted in FIG. 9 includes a means 92 forprocessing the time curve of the acceleration or the time curve of theinternal pressure to obtain an energy measure which depends on an energyimparted onto the object by the shot. This energy measure may be, e.g.,the speed at time t₁ exerted upon the movable game device by the shot.Such a situation is shown in FIG. 6 b. If it shall be assumed, again,that the object was at rest at time t₀, its speed will increase due tothe acceleration exerted at time t₀, and will rise up until time t₁. Attime t₁, for example, the football leaves the football player's leg, anda maximum speed v_(max) is reached which will then decrease again due toair friction. The instantaneous velocity at time t between t₀ and t₁ mayreadily be currently calculated by the equation shown on the right-handside of FIG. 6 b.

However, a preferred energy measure is the maximum speed at time t₁,since this energy—apart from a potential energy which will typically benegligible—is the energy transferred by the player onto the game device.If the player has transferred a lot of energy, his/her force of shot ishigh. If, on the other hand, the player has transferred little energy,his/her force of shot was low, provided that for both cases othercircumstances of the game device, for example the internal pressure, arecomparable, as will be explained in detail later on with reference toFIG. 8.

Thus, means 92 may calculate, for example, the maximum speed as anenergy measure, or may even calculate, using the ball mass, the energyassociated with the maximum speed and referred to as E_(max).

The device depicted in FIG. 9 further comprises a means 94 for providinginformation about the shot force on the basis of the energy measure. Thefunctionality of means 94 will be explained with reference to FIG. 6 eand may in this case be simply an allocation table which maps the energymeasure calculated to a scale between, e.g., 1 and 10, as in the case ofFIG. 6 e, or to an open-ended scale or to a tendency indication.

A tendency indication would consist in that a comparison of the currentenergy measure with a previously determined energy measure which wasassociated with another player is performed so as to be able to state,as the tendency indication, i.e. as information about the shot force,that the shot force of the current player was larger, equal to orsmaller than the shot force of the previous player.

Mapping the energy measure to force-of-shot information in such a mannermay be conducted using any energy measures desired, i.e. even in theevent that the force as is depicted in FIG. 6 c as a curve over time isevaluated. Thus, the force curve is proportional to the accelerationcurve, to be precise with the mass of the movable game device as theproportionality constant. The curve of the force over time also providesan energy measure which could be calculated, for example, by integratingthe force over time.

Alternatively, as is shown in FIG. 6 d, the directional force exerted onthe ball may also be measured as a function of the locus on which theball moves during the shot. Thus, the force at the location point x=0,at which the ball is located before it is hit by the player's leg, willincrease to a high value which will fall down to a certain value. Theball leaves the player's foot at the location point s₀ on the locus, sothat no more driving force is exerted on the ball, but only decelerationforces which are present due to the air friction and which, however, arenot taken into account in FIG. 6 d.

Thus, an energy measure also represents the integration of the forcemeasured (acceleration) across the locus covered by the ball. The locusmay be measured, for example, at the same time with the accelerationsensor within the ball if the acceleration sensor is an accelerationsensor which operates in a three-dimensional manner and is sensitive interms of direction. Alternatively, the locus of a projectile may also becalculated in different manners, such as by using highly accuratesatellite- or ground-based positioning systems or by accessingpredetermined tables. However, micromechanical positioning systems usingvibrating gyroscopes may also be employed for determining the locus soas to be able to numerically evaluate the integral depicted in FIG. 6.

However, the preferred embodiment of the present invention is to providea pressure sensor within the movable game device. When the movable gamedevice is shot, it could have a pressure curve as is qualitativelydepicted in FIG. 7. At a time t₀, the object hits the movable gamedevice, which will lead to a pressure increase in the movable gamedevice, since the movable game device is deformed by the objectimpacting the movable game device. This pressure increase will thenincrease up to a maximum pressure p_(max) and will then decrease againso as to diminish again down to the pressure at rest around time t₁which is characterized in that the movable game device has no morecontact with the object.

In accordance with the invention, it has thus been found out that theintegral regarding the pressure change, i.e. the area fill within thearea shaded in FIG. 7, is connected to the energy exerted on the ball,so that the time curve of the pressure may advantageously be employedfor determining the force of the shot.

The utilization of a pressure sensor is particularly advantageous,compared to an acceleration sensor, since the pressure sensor may beconfigured in a simple manner and to be robust, in comparison with anacceleration sensor which, e.g., has large masses of bending beams. Inaddition, it is inherent for a pressure sensor not to emit a directionalquantity, but to emit a non-directional quantity if it is arrangedwithin the movable game device, which in acceleration sensors could onlybe achieved by expensive provision of an acceleration sensor array whichmust be sensitive in three spatial directions. On the other hand, onesingle pressure sensor is sufficient to provide a pressure curve of theinternal pressure of the movable game device.

Thus, utilization of a pressure sensor provides a maintenance-free,robust and, at the same time, low-cost possibility of measuring thepressure curve within a movable game device and of obtainingforce-of-shot information, as will be set forth later on with referenceto FIGS. 8 and 10.

In a preferred embodiment of the present invention, the pressure curveover time is integrated between t₀ and t₁, specifically in accordancewith the equation as is shown in FIG. 7. This shows that what isintegrated is not the absolute pressure curve, but the curve of thepressure change in comparison to the pressure at rest, p₀. However, itwould also be possible to integrate the absolute pressure curve so asthen to subtract area 97 following the integration. This results simplyfrom the product of time duration Δt and the pressure at rest.

As may be seen from FIG. 8, the shot force is highly dependent on thelevel of the pressure at rest. This result from FIG. 8 on the basis ofthe various parameter curves, one parameter curve 97 being plotted for asmall pressure at rest, p₀, whereas a different parameter curve isplotted for a high pressure p₀ at 98. In particular, the x axis of thegroup of curves of FIG. 8 represents the integrated pressure change as ameasure of the energy, i.e.—calculated in physical units—a measure whichhas (Pascal times seconds) as a unit. In illustrative terms, area 96 ofthe curve shown in FIG. 7 is plotted over the x axis. If one assumes aball having a small internal pressure, a force-of-shot value will resultalong the straight line depending on how hard the ball was hit, i.e. howhigh the shot force is. If, on the other hand, a highly inflated ball isused for playing, a very much higher force of shot has been obtained asa measure of the energy, with the same integrated pressure change, incomparison with curve 97. This is due to the fact that a highly inflatedball is deformed only to a small degree even by a very hard shot,whereas a ball inflated to a very small degree is deformed by arelatively soft shot already, the deformation corresponding to theintegrated pressure change.

Alternatively or in addition, the maximum pressure p_(max) of thepressure curve over time may also be determined by means 92 of FIG. 9.Specifically, one may assume, for simpler evaluations, that the curve ofthe pressure over time, i.e. the manner in which the shot impacts theobject, is assumed to be roughly the same for all shots, such that thensolely the maximum value will be decisive. In this case, a group ofstraight lines would be provided which is similar to the group of curvesin FIG. 8 but which would not have, as the x axis, an integratedpressure change as the measure of the energy, but the maximum pressure.

As another alternative, one could also determine the time duration ofthe curve of the pressure deviation which, if typical pressure curvesare taken to be approximately the same with regard to their shapes, isalso a measure of the energy imparted on the game device during theshot.

In a preferred embodiment of the present invention, the internalpressure at rest p₀ is initially determined in a step 100, as isdepicted in FIG. 10. This determination may either occur prior to orafter the shot and is used to select one of the curves in the group ofcurves of FIG. 8. In addition, the pressure change is integrated overtime in a step 102, specifically from time t₀ to time t₁, using thetemporal pressure curve p(t) determined in a step 101. Thus, theintegration regarding the pressure change or regarding the pressuredeviation from the pressure at rest, set forth in FIG. 102, provides theenergy measure which will then be used to determine a value on theparameter curve selected. Preferably, the access made to a tablecomprising a group of curves is conducted, in a step 103, such that athree-dimensional table is given which comprises groups of three values,a first value of the group of three being the pressure at rest p₀, asecond value of the group of three being the integrated pressure change,and a third value then being the shot force as is plotted on the y axisof FIG. 8. This force-of-shot information is provided by step 103. Whencomparing FIG. 9 and FIG. 10, it is obvious that steps 100 and 101 areperformed by means 90, that step 102 is performed by means 92, and thatstep 103 is performed by means 94.

Depending on the implementation of the inventive system, i.e. on thediversity required, information about the type of game device which isfed in at 104 may also be taken into account in step 103. For example,the shot force may depend on whether the ball is a tennis ball or afootball. In addition, the shot force will vary from brand to brand.This is relevant particularly when the “ideal range” of the ball, whichwill then also depend on the surface of the ball, is taken as the shotforce. A smoother surface of the ball has a smaller air resistance, sothat with the same energy transmitted, the shot force—measured inmeters—will be higher than that of a ball having a rougher surface.Nevertheless, both force-of-shot results depend on the energy impartedon the ball, and additionally depend on the type of game device fed invia line 104.

Depending on the implementation, all or only some of the componentsshown in FIG. 9 will be arranged within the game device itself or withina central device located at a distance from the game device.

In the first embodiment of such a system, only an acceleration sensor ora pressure sensor configured to store a time curve of acceleration orpressure will be located within the game device itself. This time curveof acceleration or pressure may then be transferred, e.g. via a radiotransmitter, to a receiver which could be present with the player in theform of a watch, for example. Alternatively, the ball need notnecessarily have a radio sensor but may have an output interface which,when the ball is placed into a specifically configured docking station,will read out the stored curves of acceleration or pressure. Then, theprocessing in block 92 and the provision of force-of-shot information inblock 94 would take place in an external station, such as the player'swatch or in a central receiving station on a football pitch, etc.

Alternatively, both the functionality of means 90 and means 92 may beintegrated into the ball, and the ball already supplies the energymeasure to an external receiving station. This results in that less datamust be transferred from the ball to the outside, but that moreprocessor power is required within the game device.

Alternatively, all means 90, 92, 94 may be implemented within the mobilegame device, so that only the information about the shot force isindicated by the ball even in a direct manner, or is output via anoutput interface which may be, e.g., a radio interface or a contactinterface.

The system depicted in FIG. 9 also includes the functionality of theexternal receive interface 6 if only one sensor is present within theball and if the ball outputs the time curve of the acceleration orinternal pressure. Then, means 90 for providing a time curve ofacceleration or internal pressure of FIG. 9 is an input interface of theexternal calculator which additionally also comprises means 92 and means94.

For example, the inventive device for measuring the shot force may bearranged and implemented fully within the mobile game device or fullyoutside the game device or partly within and partly outside the mobilegame device.

In this sense, the method for measuring a force of shot exerted on themovable game device in such a partial implementation both includes thegame device and the evaluation device or only the game device or onlythe evaluation device.

The invention thus provides detection of the shot force and the flyingspeed of a game device 7 which may be determined therefrom. Thus, in afootball game there is often the question of who has the “hardest” shot.In particular for this embodiment, but also for the other embodimentsthere is the possibility of integrating the evaluation unit 13 also intothe assembly 15 within the game device 7. A sensor measuring the shotforce may be mounted in game device 7. This sensor is preferably apressure sensor 10 or an acceleration sensor. The information of thissensor is measured by an internal microcontroller and transferred, forexample, to display unit 14 on data detection device 12 of the player.For determining the shot force, it is necessary to measure the energythe ball has been imparted during the shot. To this end, the evaluationunit 13 has means for detecting the pressure, determined by pressuresensor 10, over time or for detecting the acceleration detected by theacceleration sensor. In addition, provision is made for calculatingmeans for calculating the force applied to ball 7 on the part of player6 using the pressure curve or acceleration curve.

With the acceleration sensor, the acceleration is measured directly andreported to the microcontroller within game device 7. Saidmicrocontroller calculates the force that has acted upon the ball fromthe known mass of the ball and the acceleration measured. Thesecalculations also include the aerodynamics and the time curve of theenergy transferred to the ball. The calculation comprises not onlytransferring the overall energy to the evaluation unit 13, but alsocomprises transferring the time curve of the energy transferral to theball.

In the alternative use of a pressure sensor 10, one measures how theinternal pressure of the ball increases during a shot. These pressurechanges and the associated time curve allow the microcontroller withinthe ball to determine the force that has been exerted on the ball. Usingthe pressure measurement, it is possible to ascertain how, much the ballwas deformed. The higher the level of deformation, the larger the shotforce. To this end, the peak value and the pressure curve of theinternal pressure are measured using pressure sensor 10. Using a groupof curves, the energy supplied to the ball is measured. For example, thegroup of curves may be determined in advance in a empirical manner, bymeans of a shooting system and is different for each type of ball.

Then the shot force may be determined in very accurately from the energytransferred and the time curve. Beside the shot force, the overallenergy may also be displayed. This allows to obtain information aboutthe type of shot. Thus, the ball may be played with much more precisionon an even energy supply. Thus, if the duration of the energy supply isdisplayed additionally, for which purpose additional detection means maybe provided, this may also be trained.

The energy may be used to infer the flying speed the ball has obtained.To this end, the weight and aerodynamics of the ball are taken intoaccount. The flying speed determined is the value that is reached whenthe ball may fly off freely after the shot. In addition to the action offorce, the time of the ball being hit, and the time of the ball touchingdown may also be determined using pressure sensor 10 and/or theacceleration sensor. By means of the force information and the timeduration of the flight, it is quite readily possible to calculate thedistance the ball must have flown.

In addition, components such as at least one Hall sensor 16, at leasttwo magneto-resistive sensors or at least two coils may be provided fordetermining the rotational speed of game device 7. This information maybe used for training so-called “curling crosses” in football. To thisend, it is important for the user to immediately get a feedback abouthis/her shot. For this purpose, the rotational speed within the ball ismeasured and transmitted via radio 1 to the player's 6 data detectiondevice 12. The components are to be arranged such that during theirmovement when the game device 7 is rotating in an energy field, amodulation frequency determinable by the evaluation unit 13 will resultwhich can be converted into the rotational speed.

For example, the sensor, e.g. the Hall sensor 16, measures the earth'smagnetic field and determines the field strength. When the ball rotates,the field strength undergoes a modulation. The frequency of themodulation is directly proportional to the rotational speed of the ball.During the measurement of the earth's magnetic field, the directionalvector of the magnetic field is determined. The rotation of this vectoris proportional to the rotation of the ball. Alternatively, the fieldstrength may be measured with magneto-resistive sensors as resistorsdepending on the magnetic field. They may be connected to form a bridge.The output signal of the bridge may be amplified using a differentialamplifier. The output voltage is a direct measure of the field strengthof the magnetic field. For the purposes of measuring the rotation,neither a linearity of the voltage nor a determination of the directionof the field is required. When the ball rotates, the output voltage hasan alternating voltage superimposed on it, the frequency of which is therotational frequency of the ball. The frequency of this alternatingvoltage is the rotational frequency of the ball. Evaluation of thisvoltage may either be performed discretely via an analog circuit orusing a microcontroller. To obtain a signal that can be evaluated foreach possible axis of rotation of the ball, two sensors offset by 90°are used.

The field strength may also be measured using the Hall sensor 16. Hallsensors generate a voltage in proportion to the field strength. Thisvoltage may be amplified using a differential amplifier. The outputvoltage is a direct measure of the field strength of the magnetic field.For the purposes of measuring the rotation, neither a linearity of thevoltage nor a determination of the direction of the field is required.When the ball rotates, the output voltage has an alternating voltagesuperimposed on it, the frequency of which is the rotational frequencyof the ball. Here, too, two sensors are preferably arranged such thatthey are offset by 90 degrees relative to one another.

Alternatively, it is also possible to make coils rotate in a magneticfield, so that a voltage is induced in the coils. The frequency of thevoltage is proportional to the rotational frequency. However, thevoltage must be amplified and filtered, since the coils may also act asantennas. Here, too, a discrete evaluation or an evaluation via themicrocontroller is possible, and preferably two coils are arranged suchthat they are offset by 90 degrees relative to one another.

To determine the rotational speed, radio transmitters may also be used.In this case, the change of the field strength of any radio transmitter,for example a medium-wave transmitter, is used. The frequency of thechange in field strength is proportional to the rotational frequency.Beside a dipole, a coil or a ferrite antenna may be used as an antenna.Since there are enough active long-, medium-, and short-wavetransmitters in each country, there is no need in the system to operateone's own transmitters. If transmitters having a relatively highfrequency are to be used as the reference, a dipole antenna is apossibility, which dipole antenna may be deposited, for example, on theball's electronic system or even on the ball's envelope in the form ofconductive traces. A frame antenna is suitable for low frequencies. Itmay be deposited as a coil in the form of conductive traces for assembly15 of the ball's electronic system. A ferrite antenna is suitable forlow frequencies. It may be constructed to be very small and willnevertheless generate a relatively large output signal. With allantennas it is necessary for two receive directions to be built up, sothat a signal can be measured at any axis of rotation. The only thingthat is important with signal measurement is the field strength. Forthis purpose, an amplifier having a high level of dynamics is necessary.The amplification should be logarithmic, for example, so that the A/Dconverter of the microcontroller need not be too wide.

An extremely low-power microcontroller takes on the data and the controlof the ball's electronic system. Said microcontroller is woken up at thestart of the game. If the microcontroller has not observed any game fora relatively long period, it will automatically switch off. The maintask of microcontroller 11, which may be integrated in the datadetection device in the game device as well as, or in addition to,microcontroller 11, is to process the data such that it can betransmitted via radio 1 with as little energy as possible. The data ispreferably transmitted several times via radio, e.g. via a 2.4 GHz radiolink, so as to be able to correct any errors.

Current supply may be realized in two known ways. On the one hand, onemay use an accumulator, which, however, requires charging equipment. Onthe other hand, one may use a primary battery 21 within the datadetection device and a primary battery 22 within game device 7, it notbeing possible, however, for the latter to be replaced within the ball.

In the accumulator version, a charging coil is mounted within the ball,using which the accumulator may be loaded in an inductive manner. Withthe version including battery 22, the ball is supplied using lithiumbatteries. The capacitance is designed such that the functionality ofthe electronic system is ensured for 1000 hours. With an average playingtime of 1 hour per day, the battery would last for three years.

Within data detection device 12, a transceiver is integrated as areceive unit 2. Said transceiver receives the data from the ball and/orcan establish a connection to other data detection devices in order toexchange data. Transmission and reception of data takes place, e.g.,within the 2.4 GHz band.

The transceiver may receive and transmit data. Thus, it is possible tocouple the data detection devices to one another. Thereby, the ballcontacts can be transmitted to the other data detection devices duringthe game, so that a very accurate statistical set of data will becreated in the network so as to be able to judge the game. If need be,it is also possible, by means of the data transmission, to facilitatesmall computer games in which the users may play in a networked manner.

The data within data detection device 12 is processed using a relativelylarge microcontroller 11. This microcontroller is extremely low in itspower consumption. The data is exchanged via the transceiver andvisualized on a display unit 14.

The data processed is displayed using a graphic display. The display hasan integrated controller, to which the microcontroller is connected.Operation is effected via several keys 20, the function of which isdynamic.

The current supply of data detection device 12 must be highlypower-saving. Battery 21 may be replaced. Microcontroller 11 and thedisplay are extremely power-saving. Data transmission is designed suchthat the transceiver is in operation only for a very short time in eachcase.

With the ball version including an accumulator, a charging station isnecessary. Since there is no line connection to the ball's electronicsystem, it is necessary to inductively charge the ball in a knownmanner. To this end, the charging station comprises a transmitter coilwith which the energy is transferred into the ball.

In order to be able to communicate with other evaluation units, it isnecessary to convert the radio communication to a different protocol.Since it is with a probability of 99% that a common PC will be used, aconversion in accordance with, e.g., USB is envisaged.

A more detailed description will be given below of the interactingcomponents of the preferred concept, i.e. of the movable device of FIG.4 a and FIG. 4 b, and of the receiver device of FIGS. 5 a and 5 b.Movable device 7 contains a detector 23 which may be, e.g., the pressuresensor 10 of FIG. 3 and which detects if ball 7 is touched. However,detector 23 may include a contactless sensor which operates in anelectric, acoustic, optical or electromagnetic manner and detects, forexample, whether a magnetic or electric field of any kind which isgenerated, e.g., by a respective transmitter within a football player'sshoe approaches the ball. Detector 23 is configured to detect that anobject, i.e., for example, a leg, a foot, a shoe, a racket, a bat, orthe like, is positioned in the vicinity of or at the game device.

In addition, mobile device 7 includes a transmitter module 24 configuredto transmit a first signal having a first signal speed, and to furthertransmit a second signal having a second signal speed which is smallerthan the first signal speed. The transmitter module is configured totransmit the first and second signals in response to a detector outputsignal, as is shown by signal arrow 25 in FIG. 4 a.

As has already been set forth, detector 23 is a touch sensor configuredto detect the movable device being touched by the object. Such a touchsensor is, for example, the pressure sensor, however, it is also anacceleration sensor or any other sensor detecting whether the objectengages with the surface of game device 7. Alternatively, the detectormay also be configured as a contactless sensor which, as has been setforth, detects in some way that there is an object in the vicinity ofthe movable device. A contactless sensor which detects whether an objectis located at a predetermined distance, which is smaller than or equalto 10 cm, from the movable device is suitable for specific embodiments.Then it is very likely for the object to actually touch the movabledevice, since the only aim is to cause the object to touch the movabledevice, for example when one thinks of a football as the movable device,or of a tennis ball. One may assume, with a probability of almost onehundred percent, that once the object is located within thepredetermined distance, the object will eventually have contact with themovable device.

The transmitter module is configured to send two signals havingdifferent signal speeds. Preferably, a radio signal generated by radiotransmitter 3 is used as the first, fast signal. The second signal isgenerated by a sound transmitter 26 preferably configured as anultrasonic transmitter. Both transmitters are controlled by the detectorsignal supplied via line 25, so as to send both signals at the same timeor essentially at the same time, i.e. within a period of, e.g., 1 to 2ms, in response to the detector signal. Alternatively, however, thetransmitters may be configured such that the radio transmitter sends thefirst signal at a specific moment determined by detector signal 25, andthat the ultrasonic transmitter then waits for a predetermined timeduration before the ultrasonic signal is transmitted. Here, thereception of the radio transmitter would also not immediately cause achronometer to be activated on the receiver side, but the chronometerwould be activated within a predefined time duration upon reception ofthe first signal, i.e. not immediately upon reception of the firstsignal, but depending on the reception of the first signal.

Alternatively, ball-contact detection could also be used to initiallysend the ultrasonic signal and then, after a specific time duration, theradio signal which will then overtake the ultrasonic signal, as it were,so that on the receiver side, a very short predetermined time durationis sufficient, within which the radio signal and the ultrasonic signalwill arrive. However, it is preferred that both transmitters send theirsignals at the same time and that an accordingly longer predeterminedtime duration be employed on the receiver side, and/or that on thereceiver side, the chronometer be started immediately upon reception ofthe radio transmitter.

The predetermined time duration depends on the difference of the speedsof the first, fast signal and the second, slow signal. The smaller thisdifference in speeds, the smaller the predetermined time duration thatmay be selected. The larger the difference in speeds, the longer thepredetermined time duration that must be set. In addition, thepredetermined time duration depends on whether the first and secondsignals are really sent at the same time, or whether the first andsecond signals are sent with an offset in time, a delay in the secondsignal with regard to the first signals leading to a delay in the startof the predetermined time duration, while a delay of the first signalrelative to the second signal leads to a smaller predetermined timeduration. In general, however, predetermined time durations of less than5 ms are preferred, as has already been set forth.

As is depicted in FIG. 5 b, on the receiver side, the receiver module isin connection with a detector 28 which may be coupled to a memory 29 orwhich may be coupled to a further radio transmitter within the receiverdevice, which is not shown in FIG. 5 a, however. The detector and memory29 are preferably contained within evaluation unit 13 of FIG. 3. Thereceiver device overall shown at the bottom of FIG. 3, or the receiverdevice shown in FIG. 5 a, is preferably configured such that it isintegrated into a watch, or has the shape and looks of a watch, so thatit may readily be worn by, e.g., a football player or a tennis playerwithout said player being adversely affected in practicing his/hersport. Generally speaking, the receiver device is mountable to theobject whose vicinity to the mobile device is detected by detector 23 inFIG. 4 a, and comprises an appropriate fixing device which is not shownin FIG. 5 a but which has the shape, for example, of a watchstrap, afixture for a watchstrap, a clip or a different mounting device whichmay be secured in some way to the object and/or to a player.

The receiver module 2 is configured to receive the first signal havingthe first signal speed and the second signal having the second signalspeed, which is smaller than the first signal speed. In addition,detector 28 is configured to provide a detector signal indicatingwhether the second signal has been received within a predetermined timeduration since reception of the first signal. In addition, the detectoris preferably coupled to memory 29 which is configured to store themoment when the detector provides the detector signal. Alternatively, afurther transmitter may be present instead of the memory, thetransmitter being configured to send the detector signal to a centraldetection point where, e.g., an online evaluation of ball contacts forthe individual players is performed.

Such an online detection point would be, for example, a receiverarranged somewhere in the vicinity of a football pitch. In this case,any receiver device would send, on the output side, a contact with themovable device together with an identification for the player wearingthe receiver device, so that indisputable statistical data can beobtained as to which player had how many ball contacts.

Recently, one has found that such information about ball contacts etc.are increasingly detected, shown and provided to a large audience and/orthe commentator, for example, in football matches, so as to increase theinformation content for the viewers.

In the implementation with memory 29, for example, no central receiverdevice is required on the football pitch. Instead, the memory may beevaluated, for example, at half-time or at the end of the game, or in acontactless manner during the game without any interaction on the partof any player, so as to either obtain a count value for each playerindicating how often the player had contact with the movable device. Inthis case, player 29 would be implemented as a counter incremented by 1during each detection of the detector signal. Alternatively or inaddition, the memory may also detect an absolute time of a clock, orwatch, preferably contained within the receiver device and depicted at30 in FIG. 5 b. Then the memory would store a sequence of moments intime which may then be evaluated to be able to establish, for eachplayer, a “ball-contact profile” over time. Here, it may also bepossible to subsequently correct any erroneous detections that may havetaken place, for example if one found out that more than two players hadcontact with the ball at the same time. Simultaneous contact of twoplayers is relatively likely, for example when one thinks of a “50/50ball”. However, a contact of, e.g., three players with the ball at thesame time, becomes very unlikely in football. However, in tennis, forexample, a contact of two tennis rackets at the same time is alreadyimpossible, so that here, additional information about typicalsituations, in a sport, involving the movable game device may be used toperform an evaluation wherein errors may be eliminated.

FIG. 5 b shows a more specific embodiment of the receiver shown in FIG.5 a. The receiver module comprises, on the one hand, a radio receiver 32for receiving the first, fast signal, and an ultrasonic receiver 32 forreceiving the second, slower signal. Radio receivers and ultrasonicreceivers may also be configured differently, as long as they receiveany signals having different signal speeds. Depending on a radio signalreceived, a detector 28 activates a chronometer 31 via a start line 35.Once a predetermined time duration and/or the predetermined time periodhas expired, the chronometer is stopped, which will typically beperformed such that the chronometer 31, which is set to thepredetermined time period, will provide a stop signal to the detectorvia a stop line 36.

If the detector detects an ultrasonic signal upon receiving the stopsignal, no detector signal will be output on a line 37. In this case, itis actually assumed that the receiver device is located at such a longdistance from the movable device that it is very likely for the movabledevice to not have been hit. However, if an ultrasonic signal isreceived by the detector before receiving the stop signal, i.e. beforethe predetermined time period has expired, the detector signal 37 willbe output, which will then be stored by the memory, the memory being,for example, a counter incremented by 1 by the detector signal.

Alternatively, the detector signal is supplied to a clock, or watch,which performs absolute time measurement, which, e.g., may be an actualabsolute time of the day, but which, e.g., is also an absolute timewhich begins, e.g., at the beginning of the game and is thus notdirectly an absolute time, but renders one minute of, e.g., a footballgame. At the time of the detector signal, clock 30 will then provide itscurrent reading via a data line 38, so that the memory is then able tostore this specific moment in time. A random evaluation of the players'activity may be performed by means of an evaluation unit having aninterface, as may be implemented, for example, by display unit 14 inFIG. 3 or in FIG. 5 b, which cooperates, in particular, withmicrocontroller 11 of FIG. 3.

Depending on the circumstances, the inventive methods may be implementedin hardware or in software. The implementation may be on a digitalstorage medium, in particular a disk or a CD with electronicallyreadable control signals which may cooperate with a programmablecomputer system in such a manner that the respective method isperformed. Generally, the invention thus also consists in a computerprogram product having a program code, stored on a machine-readablecarrier, for performing the inventive method, when the computer programproduct runs on a computer. In other words, the present invention isthus also a computer program having a program code for performing themethod of converting, when the computer program runs on a computer.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents whichfall within the scope of this invention. It should also be noted thatthere are many alternative ways of implementing the methods andcompositions of the present invention. It is therefore intended that thefollowing appended claims be interpreted as including all suchalterations, permutations, and equivalents as fall within the truespirit and scope of the present invention.

1. A system for measuring a rotational speed of a movable game device, comprising: a magnetic field detector integrated within said movable game ball, said magnetic field detector configured to measure the earth's magnetic field and generate a voltage representing the magnetic field strength, wherein the magnetic field strength is modulated upon rotation of said movable game ball, thereby altering said voltage; an amplifier operatively coupled with said magnetic field detector, said amplifier configured for amplifying said voltage; a device processor configured for determining the rotational speed of said game ball by analyzing said voltage and alterations thereof; and an interface for providing information about the rotational speed on the basis of said voltage analysis.
 2. The system of claim 1, further comprising: a transmitter integrated within said movable game ball and operatively coupled with said device processor, said transmitter configured for communicating the voltage analysis.
 3. The system of claim 2, further comprising: a receiver coupled with said interface and with an interface processor, wherein said receiver is configured for receiving the voltage analysis from the transmitter, and wherein the interface processor is configured for translating said voltage analysis into information about the rotational speed.
 4. The system of claim 1, wherein the magnetic field detector is a magneto-resistive sensor device with bridge circuit or voltage divider generating a voltage in proportion to said magnetic field strength.
 5. The system of claim 1, wherein the magnetic field detector is a Hall sensor device generating a voltage in proportion to said magnetic field strength.
 6. The system of claim 1, further comprising: a provider for providing a time curve, which occurs when the game device is impacted by an object, of an acceleration acting upon the object, or a time curve of a pressure of the game device; a processor for processing the time curve of the acceleration or the time curve of the pressure to obtain an energy measure which depends on an energy transferred onto the object by the shot; a provider for providing information about the shot force on the basis of the energy measure.
 7. The system as claimed in claim 6, wherein the provider comprises an acceleration sensor or pressure sensor mounted to a game device, or comprises a receiver configured to obtain time curves stemming from the movable game device, or to obtain an energy measure.
 8. The system as claimed in claim 6, wherein the processor is configured to temporally integrate the time curve, a result of an integration representing the energy measure.
 9. The system as claimed in claim 6, wherein the processor is configured to examine the time curve for a maximum, a minimum, a shape, a time duration of a deviation from a normal value in a state at rest so as to obtain the energy measure.
 10. The system as claimed in claim 6, wherein the shot force is a value on a shot-force scale, and wherein the provider is configured to map a value of the energy measure to a value of the shot-force scale in accordance with a predetermined mapping specification.
 11. The system as claimed in claim 6, wherein the shot force is dependant on a distance, the movable game device would cover when hit within a specific shot angle, and wherein the provider is configured to calculate the distance covered on the basis of the energy measure, a game-device weight and a game-device friction in air.
 12. The system as claimed in claim 6, wherein the provider is configured to measure the time curve of the internal pressure, wherein the processor is configured to provide information about an internal pressure at rest prior to or after the shot, and to integrate a pressure change of the pressure over the pressure at rest in order to obtain the energy measure, and wherein the provider comprises a memory having an information about a previously determined group of curves stored therein, information about curves o being stored for various pressures, one curve including a connection between a shot force and an energy measure, and wherein the provider is configured to select a curve on the basis of the pressure at rest and to provide, on the basis of the energy measure, a shot force indicated by the curve selected.
 13. The system as claimed in claim 12, wherein the memory has a three-dimensional table stored therein, wherein a shot force is associated with different pairs of internal pressure and energy measure, and wherein the provider is configured to access the table as a function of the internal pressure and the energy measure, in order to determine the shot force.
 14. The system as claimed in claim 1, wherein the movable game device is a ball.
 15. The system as claimed in claim 12, wherein the provider comprises information about different groups of curves for different types of game devices, and wherein the provider is configured to identify, beside the internal pressure and the energy measure, also a type of the game device on the basis of an input piece of information about the type of the game device.
 16. The system as claimed in claim 15, wherein the provider for providing information about the shot force is configured to obtain a piece of information about the type of the game device via a radio signal from the game device.
 17. A movable game device comprising: a magnetic field detector integrated within said movable game ball, said magnetic field detector configured to measure the earth's magnetic field and generate a voltage representing the magnetic field strength, wherein the magnetic field strength is modulated upon rotation of said movable game ball, thereby altering said voltage; an amplifier operatively coupled with said magnetic field detector, said amplifier configured for amplifying said voltage; a device processor configured for determining the rotational speed of said game ball by analyzing said voltage and alterations thereof; and a transmitter integrated within said movable game ball and operatively coupled with said device processor, said transmitter configured for communicating the voltage analysis.
 18. A method for measuring a rotational speed of a movable game device, comprising: providing a magnetic field detector integrated within said movable game ball and operatively coupled with a processor, said magnetic field detector configured to measure the earth's magnetic field and generate a voltage representing the magnetic field strength; providing an amplifier operatively coupled with said magnetic field detector, said amplifier configured for amplifying said voltage; wherein the magnetic field strength is modulated upon rotation of said movable game ball, thereby altering said voltage; determining, using said processor, the rotational speed of said game ball by analyzing said voltage and alterations thereof; providing a transmitter within said movable game ball and operatively coupled with said processor; and transmitting, using said transmitter, said voltage analysis.
 19. The method of claim 18, further comprising: providing an interface operatively coupled with a interface processor; providing a receiver operatively coupled with said interface processor; receiving said voltage analysis via said receiver; processing said voltage analysis via said interface processor to determine information about the rotational speed of said game ball.
 20. The method of claim 18, further comprising: providing a time curve, which occurs when the game device is impacted by an object, of an acceleration acting upon the object, or a time curve of a pressure of the game device; processing the time curve of the acceleration or the time curve of the pressure to obtain an energy measure which depends on an energy transferred onto the object by the shot; providing information about the shot force on the basis of the energy measure.
 21. A computer readable memory device containing instructions for performing the method of claim
 18. 